The invention relates to an electronic system for transmitting data between a plurality of stations which are interconnected via a common bus.
In known systems of the type defined in the opening paragraph at least some of the stations have a microcontroller which controls the stations and is connected to the bus via an interface circuit constructed as a transmit/receive circuit, hereinafter also referred to as "signal converter", so as to transmit and receive information via this bus. The systems often also include a timing circuit, hereinafter referred to as "watchdog", which circuit supplies a signal to the microcontroller when it has not received a signal from the microcontroller for a time longer than a given duration. These elements, or at least some of them, are powered via a voltage regulator circuit when, for example in the case of automotive use, the available voltage is higher than the operating voltage of the elements. Under given conditions the microcontroller can set all the elements of the stations to a power-saving mode of operation, for example to spare a battery forming the power source, or the station can be restored to a normal mode of operation by local events or by signals via the bus.
External disturbances or disturbances in individual elements may give rise to undesired operating conditions. It is customary that the microcontroller detects any undesired operating conditions and takes steps to reset the station to an operating condition which is useful for the application. The microcontroller is again monitored by the watchdog and is reset to a well-defined initial state by means of a reset signal in the event of a malfunction.
An important drawback is that a continuously malfunctioning microcontroller, which neither operates correctly in the initial state, can no longer set the other elements to a well-defined default operating condition and, under given circumstances, the entire system with a plurality of stations will fail. The same situation arises when, for example, only the power supply to the microcontroller fails. Apart from failure of the entire system, effects may arise which are unfavorable for the application.
A further drawback is that in such situations the microcontroller can no longer set the relevant station to a power-saving mode because the serial data or information transmitted for this purpose via the system can no longer be evaluated in the station itself.